Bearing assembly including bearing support ring configured to reduce thermal warping during use, bearing apparatuses using the same, and related methods

ABSTRACT

Various embodiments relate to a bearing assembly including a support ring configured to reduce thermal warping under operational temperature conditions, a bearing apparatus that may utilize such a thrust-bearing assembly, and applications that incorporate the disclosed bearing apparatuses such as downhole motors in subterranean drilling systems, directional drilling systems, and many other apparatuses. In an embodiment, a bearing assembly includes a plurality of superhard bearing elements distributed circumferentially about an axis. The thrust-bearing assembly further includes a support ring having the plurality of superhard bearing elements mounted thereto. The support ring includes at least one thermal-warping-reducing feature configured to reduce a radial moment, compared to if the at least one thermal-warping-reducing feature were absent from the support ring, which is thermally induced in the support ring when the support ring and the plurality of superhard bearing elements are exposed to operational temperature conditions.

BACKGROUND

Subterranean drilling systems that employ downhole drilling motors arecommonly used for drilling boreholes in the earth for oil and gasexploration and production. A subterranean drilling system typicallyincludes a downhole drilling motor that is operably connected to anoutput shaft. A pair of thrust-bearing apparatuses also can be operablycoupled to the downhole drilling motor. A rotary drill bit configured toengage a subterranean formation and drill a borehole is connected to theoutput shaft. As the borehole is drilled with the rotary drill bit, pipesections may be connected to the subterranean drilling system to form adrill string capable of progressively drilling the borehole to a greaterdepth within the earth.

Each thrust-bearing apparatus includes a stator that does not rotate anda rotor that is attached to the output shaft and rotates with the outputshaft. The stator and rotor each includes a plurality of bearingelements that may be fabricated from polycrystalline diamond compacts(“PDCs”) that provide diamond bearing surfaces that bear against eachother during use.

In operation, high-pressure drilling fluid is circulated through thedrill string and power section of the downhole drilling motor, usuallyprior to the rotary drill bit engaging the bottom of the borehole, togenerate torque and rotate the output shaft and the rotary drill bitattached to the output shaft. When the rotary drill bit engages thebottom of the borehole, a thrust load is generated, which is commonlyreferred to as “on-bottom thrust” that tends to compress and is carried,at least in part, by one of the thrust-bearing apparatuses. Fluid flowthrough the power section may cause what is commonly referred to as“off-bottom thrust,” which is carried, at least in part, by the otherthrust-bearing apparatus. The drilling fluid used to generate the torquefor rotating the rotary drill bit exits openings formed in the rotarydrill bit and returns to the surface, carrying cuttings of thesubterranean formation through an annular space between the drilledborehole and the subterranean drilling system. Typically, a portion ofthe drilling fluid is diverted by the downhole drilling motor to cooland lubricate the bearing elements of the thrust-bearing apparatuses.

The on-bottom and off-bottom thrust carried by the thrust-bearingapparatuses can be extremely large. The operational lifetime of thethrust-bearing apparatuses often determines the useful life of thesubterranean drilling system. Therefore, manufacturers and users ofsubterranean drilling systems continue to seek improved bearingapparatuses to extend the useful life of such bearing apparatuses.

SUMMARY

Various embodiments of the invention relate to a bearing assemblyincluding a support ring configured to reduce thermal warping underoperational temperature conditions, a bearing apparatus that may utilizesuch a bearing assembly, and systems that incorporate the disclosedbearing apparatuses such as downhole motors in subterranean drillingsystems, directional drilling systems, and many other apparatuses. Byreducing thermal warping in the support ring when it is exposed toelevated operational temperature conditions, the extent to whichrespective bearing surfaces of the bearing assembly are displaced out ofplane from each other may be limited to thereby allow for hydrodynamicoperation when used in a bearing apparatus.

In an embodiment, a bearing assembly includes a plurality of superhardbearing elements distributed circumferentially about an axis. Thebearing assembly further includes a support ring having the plurality ofsuperhard bearing elements mounted thereto. The support ring includes atleast one thermal-warping-reducing feature configured to reduce a radialmoment, compared to if the at least one thermal-warping-reducing featurewere absent from the support ring, which is thermally induced in thesupport ring when the support ring and the plurality of superhardbearing elements are exposed to operational temperature conditions.

In an embodiment, a bearing apparatus includes two bearing assemblies.At least one of the two bearing assemblies may be configured as any ofthe disclosed bearing assembly embodiments that include a support ringconfigured to reduce thermal warping.

Other embodiments include downhole motors for use in drilling systemsand subterranean drilling systems that may utilize any of the disclosedbearing apparatuses.

Features from any of the disclosed embodiments may be used incombination with one another, without limitation. In addition, otherfeatures and advantages of the present disclosure will become apparentto those of ordinary skill in the art through consideration of thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate several embodiments of the invention, whereinidentical reference numerals refer to identical elements or features indifferent views or embodiments shown in the drawings.

FIG. 1A is an isometric view of an embodiment of a thrust-bearingassembly including a support ring having a plurality ofradially-extending slots therein configured to reduce thermal warpingunder operational temperature conditions.

FIG. 1B is a top plan view of the thrust-bearing assembly shown in FIG.1A.

FIG. 1C is a side cross-sectional view of the thrust-bearing assemblyshown in FIG. 1B taken along line 1C-1C.

FIG. 1D is the side cross-sectional view of the thrust-bearing assemblyshown in FIG. 1C depicting how the support ring warps under operationaltemperature conditions.

FIG. 2A is an isometric view of an embodiment of a thrust-bearingassembly including a support ring configured to accommodate minorthermal warping of another thrust-bearing assembly with which it isoperably assembled.

FIG. 2B is a top plan view of the thrust-bearing assembly shown in FIG.2A.

FIG. 2C is a side cross-sectional view of the thrust-bearing assemblyshown in FIG. 2B taken along line 2C-2C.

FIG. 2D is a simplified side cross-sectional view of the thrust-bearingassembly shown in FIG. 2C depicting how the support ring can bend.

FIG. 3A is a side cross-sectional view of an embodiment of athrust-bearing apparatus that may include a stator configured as thethrust-bearing apparatus shown in FIGS. 1A-1D and a rotor configured asthe thrust-bearing apparatus shown in FIGS. 2A-2D.

FIG. 3B is an enlarged cross-sectional view of the thrust-bearingapparatus shown in FIG. 3A illustrating how the support ring of therotor can bend to accommodate minor thermal warping of the support ringof the stator.

FIG. 4A is an isometric view of an embodiment of a thrust-bearingassembly including a support ring having a plurality ofradially-extending slots therein configured to reduce warping underoperational temperature conditions to accommodate thermal warping ofanother thrust-bearing assembly.

FIG. 4B is a top plan view of the thrust-bearing assembly shown in FIG.4A.

FIG. 4C is a cross-sectional view of the thrust-bearing assembly shownin FIG. 4B taken along line 4C-4C.

FIG. 5 is a side cross-sectional view of an embodiment a thrust-bearingassembly having a bi-material support ring that is configured tocompensate for thermal warping due to a thermal gradient the bi-materialsupport ring.

FIG. 6 is a schematic isometric cutaway view of an embodiment of asubterranean drilling assembly that may include one or more of thedisclosed thrust-bearing apparatuses.

DETAILED DESCRIPTION

Various embodiments of the invention relate to a bearing assemblyincluding a support ring configured to reduce thermal warping underoperational temperature conditions and a bearing apparatuses that mayutilize such a bearing assembly. By reducing thermal warping in thesupport ring when it is exposed to elevated operational temperatureconditions, the extent to which respective bearing surfaces of thebearing assembly are displaced out of plane from each other may belimited to thereby allow for hydrodynamic operation (under certainconditions) when used in a bearing apparatus. The disclosed bearingapparatuses may be used in a number of applications, such as downholemotors in subterranean drilling systems, directional drilling systems,pumps, transmissions, gear boxes, and many other apparatuses.

FIGS. 1A-1C are isometric, top plan, and side cross-sectional views,respectively, of an embodiment of a thrust-bearing assembly 100. Thethrust-bearing assembly 100 may form a stator or a rotor of athrust-bearing apparatus used in a subterranean drilling system. Thethrust-bearing assembly 100 includes a support ring 102 defining anopening 104 through which a shaft (not shown) of, for example, adownhole drilling motor may extend. The support ring 102 may be madefrom a variety of different materials. For example, the support ring 102may comprise carbon steel, stainless steel, tungsten carbide, or anothersuitable material. The support ring 102 includes a plurality of recesses110 (FIG. 1C) formed therein.

The thrust-bearing assembly 100 further includes a plurality ofsuperhard bearing elements 106 that are distributed circumferentiallyabout a thrust axis 108 along which a thrust force may be generallydirected during use. As used herein, a superhard bearing element is abearing element including a bearing surface that is made from a materialexhibiting a hardness that is at least as hard as tungsten carbide.Although the superhard bearing elements 106 are illustrated as beingcylindrical, in other embodiments, the superhard bearing elements 106may be non-cylindrical such as oblong or other non-cylindrical geometry.Each superhard bearing element 106 is partially disposed in acorresponding one of the recesses 110 (FIG. 1C) of the support ring 102and secured partially therein via brazing, press-fitting, fastening witha fastener, or another suitable technique. Each superhard bearingelement 106 includes a bearing surface 112 that is substantially planarand generally lies in a common plane P (FIG. 1C) with the bearingsurfaces 112 of the other superhard bearing elements 106. The superhardbearing elements 106 may be pre-machined to tolerances and mounted inthe support ring 102 and/or mounted to the support ring 102 and thebearing surfaces 112 thereof and planarized (e.g., by lapping and/orgrinding) so that the bearing surfaces 112 are all substantiallycoplanar. Optionally, one or more of the superhard bearing elements 106may exhibit a peripherally-extending edge chamfer 114. However, in otherembodiments, the edge chamfer 114 may be omitted.

The support ring 102 further includes a plurality ofthermal-warping-reducing features 116, which compared to if they wereabsent, increase the compliance of the support ring 102 and reduce aradial moment that is thermal induced in the support ring 102 due to atemperature gradient in the support ring 102. The temperature of thethermal gradient in the support ring 102 increases with distance towardthe bearing surfaces 112 of the superhard bearing elements 106 (i.e.,the temperature is hottest at the bearing surfaces 112). The thermalgradient is generated by the frictional heat generated at the bearingsurfaces 112 of the superhard bearing elements 106 during use. In theillustrated embodiment, each thermal-warping-reducing feature 116 isconfigured as a radially-extending slot that extends only partiallythrough the support ring 102 in a thickness direction. Eachradially-extending slot 116 may be disposed between immediately adjacentsuperhard bearing elements 106, and may be disposed circumferentiallyabout halfway between immediately adjacent superhard bearing elements106. For example, each radially-extending slot 116 may exhibit a widthof about 0.0020 inch to about 0.100 inch, such as about 0.030 inch toabout 0.050 inch, about 0.035 inch to about 0.045 inch, or about 0.010inch to about 0.040 inch. However, in other embodiments, at least one, aportion of, or all of the thermal-warping-reducing features 116 may beconfigured as a recess, a blind or through hole, or other feature thatdeparts from the depicted elongated geometry of the radially-extendingslots. As will be discussed in more detail below, the radially-extendingslots 116 increase the compliance of the support ring 102 compared to ifthey were absent. By increasing the compliance of the support ring 102,a radial moment that is thermally induced in the support ring 102 due tothe temperature gradient in the support ring 102 may also be reduced.Such a configuration may enable the bearing surfaces 112 of thesuperhard bearing elements 106 to be displaced out of the plane P (if atall) by a relatively small amount.

FIG. 1D is the side cross-sectional view of the thrust-bearing assembly100 shown in FIG. 1C depicting how the support ring 102 can warp underoperational temperature conditions. The operational temperatureconditions are temperatures commonly experienced when the thrust-bearingassembly 100 is used in a downhole drilling motor. For example, theoperational temperature conditions that the support ring 102 and thebulk of the superhard bearing elements 106 may be subjected to duringdownhole drilling operations are at least about 100° C., such as about100° C. to about 200° C. or, more particularly, about 100° C. to about150° C. Under operational temperature conditions, the support ring 102warps (e.g., twists) due to a radial moment M_(r) thermally inducedtherein due to the temperature gradient in the support ring 102, withthe temperature of the thermal gradient increasing with distance towardthe bearing surfaces 112 of the superhard bearing elements 106. At amaximum, under the operational temperature conditions, the support ring102 may warp so that the bearing surfaces 112 of the superhard bearingelements 106 may be displaced out of plane by an angle θ, such as about0.02 degrees to about 0.2 degrees. Stated another way, an outermostperipheral edge of each superhard bearing element 106 may be displacedout of plane by a distance h of about 0.00020 inch to about 0.0020 inch,such as about 0.0005 inch to about 0.0010 inch, which is also referredto as the maximum flatness.

The superhard bearing elements 106 may be made from a number ofdifferent superhard materials, such as polycrystalline diamond,polycrystalline cubic boron nitride, silicon carbide, tungsten carbide,or any combination of the foregoing superhard materials. In anembodiment, one or more of the superhard bearing elements 106 mayinclude polycrystalline diamond. In some embodiments, thepolycrystalline diamond may be leached to at least partially orsubstantially completely remove a metal-solvent catalyst (e.g., cobalt,iron, nickel, or alloys thereof) that was used to sinter precursordiamond particles that form the polycrystalline diamond. In otherembodiments, the polycrystalline diamond may be unleached and include ametal-solvent catalyst (e.g., cobalt, iron, nickel, or alloys thereof)that was used to sinter the precursor diamond particles that form thepolycrystalline diamond. In yet another embodiment (as illustrated), oneor more of the superhard bearing elements 106 may be configured as asuperhard compact with a superhard table 118 bonded to a substrate 120.For example, the superhard compact may be a PDC including acobalt-cemented tungsten carbide substrate (substrate 120) having apolycrystalline diamond table (superhard table 118) that was sintered ina first high-pressure/high-temperature process on the substrate 120 orbonded to the substrate 120 in a bonding process (e.g., a secondhigh-pressure/high-temperature process).

FIGS. 2A-2C are isometric, plan, and side cross-sectional views,respectively, of an embodiment of a thrust-bearing assembly 200, whichis suitable for use in a subterranean drilling system. Thethrust-bearing assembly 200 may form a stator or a rotor of athrust-bearing apparatus used in a subterranean drilling system. Thethrust-bearing assembly 200 includes a support ring 202 defining anopening 204 through which a shaft (not shown) of, for example, adownhole drilling motor may extend. The support ring 202 includes aplurality of recesses 206 (FIG. 2C) formed therein that are partiallydefined by a circumferentially-extending upper base 208.

The thrust-bearing assembly 200 further includes a plurality ofsuperhard bearing elements 106 that are distributed circumferentiallyabout a thrust axis 210 along which a thrust force may be generallydirected during use. Each superhard bearing element 106 is partiallydisposed in a corresponding one of the recesses 206 of the support ring202 and supported on the upper base 208. For example, each superhardbearing element 106 may be secured partially within the correspondingone of the recesses 206 of the support ring 202 via brazing,press-fitting, fastening with a fastener, or another suitable technique.Each superhard bearing element 106 includes a bearing surface 112 thatis substantially planar and generally lies in a common plane P (FIG. 2C)with the bearing surfaces 112 of the other superhard bearing elements106. The superhard bearing elements 106 may be pre-machined totolerances and mounted in the support ring 102 and/or mounted to thesupport ring 102 and the bearing surfaces 112 thereof planarized (e.g.,by lapping and/or grinding) so that the bearing surfaces 112 are allsubstantially planar coplanar.

The support ring 202 further includes an outercircumferentially-extending recess 212 that is defined by the upper base208, a circumferentially-extending flexible support 214, and a lowerbase 209. The recess 212 is positioned below the plurality of recesses206. The recess 212 increases the compliance of the support ring 202compared to if it were absent from the support ring 202. In anembodiment, the recess 212 may exhibit a thickness of about 0.250 inchto about 1.00 inch (e.g., about 0.300 inch to about 0.600 inch) andextend radially inwardly about 0.200 inch to about 0.500 inch (e.g.,about 0.200 inch to about 0.300 inch).

As shown in the simplified side cross-sectional view of FIG. 2D, theupper base 208 carrying the superhard bearing elements 106 thereon maypivot when one or more of the superhard bearing elements 106 are loaded(e.g., at or near an edge of one or more of the bearing surfaces 112 ofthe superhard bearing elements 106). As illustrated, the upper base 208may pivot radially inwardly in response to the bearing surfaces 112 ofthe superhard bearing elements 106 being loaded more at or near theinner most portion thereof so that the bearing surfaces 112 mayaccommodate the bearing surfaces of another thrust-bearing assemblybeing slightly out of plane with each other.

Any of the previously described thrust-bearing assemblies may be used ina thrust-bearing apparatus that employs two thrust-bearing assemblies.FIG. 3A is an isometric view of an embodiment of a thrust-bearingapparatus 300. The thrust-bearing apparatus 300 includes a rotor 302that is configured as the thrust-bearing assembly 100 shown in FIGS.2A-2D and a stator 304 that is configured as the thrust-bearing assembly100 shown in FIGS. 1A-1D. The rotor 302 may be attached to and rotatewith a shaft 306. While the stator 304 is shown configured as thethrust-bearing assembly 100 shown in FIGS. 1A-1D, in other embodiments,the rotor 302 may be configured as the thrust-bearing assembly 100 andthe stator 304 may be configured as the thrust-bearing assembly 200shown in FIGS. 2A-2D.

The shaft 306 may, for example, be operably coupled to an apparatuscapable of rotating the shaft 306 in a direction R (or in an oppositedirection) about a rotation axis 308, such as a downhole motor. Forexample, the shaft 306 may extend through and may be secured to therotor 302 by press-fitting or threadly coupling the shaft 306 to therotor 302, or another suitable technique. The stator 304 is notconnected to the shaft 306 and, therefore, remains stationary while therotor 302 rotates. The respective bearing surfaces 112 of the superhardbearing elements 106 of the rotor 302 are oriented to generally opposethe respective bearing surfaces 112 of the superhard bearing elements106 of the stator 304.

In operation, rotation of the rotor 302 at a sufficient rotational speedsweeps drilling fluid onto bearing surfaces 112 of the stator 304 andallows a fluid film 310 to develop between the bearing surfaces 112 ofthe stator 304 and the bearing surfaces 112 of the rotor 302. The fluidfilm 310 may develop under certain operational conditions in which therotational speed of the rotor 302 is sufficiently great and the thrustload is sufficiently low. Under such hydrodynamic operationalconditions, the pressure of the fluid film 310 is sufficient to preventcontact between the bearing surfaces 112 of the stator 304 and thebearing surfaces 112 of the rotor 302 and, thus, substantially reducewear of the superhard bearing elements 106. When the thrust loads exceeda certain value and/or the rotational speed of the rotor 302 is reduced,the fluid film 310 may not be sufficient to prevent the bearing surfaces112 of the stator 304 and the bearing surfaces 112 of the rotor 302 fromcontacting each other. Under such operational conditions, thethrust-bearing apparatus 300 is not operated as a hydrodynamic bearing.Under other operational conditions, the thrust-bearing apparatus 300 maybe operated in a mixed mode in which the fluid film 310 is onlypartially developed to help reduce, but not prevent contact of thebearing surfaces 112 of the stator 304 and the bearing surfaces 112 ofthe rotor 302. Thus, under certain operational conditions, thethrust-bearing apparatus 300 may be operated hydrodynamically and underother conditions the thrust-bearing apparatus 300 may be operated sothat the bearing surfaces 112 contact each other during use or apartially developed fluid film is present between the bearing surfaces112 during use. However, the superhard bearing elements 106 aresufficiently wear-resistant to accommodate repetitive contact with eachother, such as during start-up and shut-down of a subterranean drillingsystem employing the thrust-bearing apparatus 300 or other operationalconditions not favorable for forming the fluid film 310.

Referring to FIG. 3B, which is an enlarged side cross-sectional view ofFIG. 3A, illustrating how the support ring 202 of the rotor 304 can bendto accommodate minor thermal warping of the support ring 102 of thestator 304. The configuration of the support ring 202 of the rotor 302enables the support ring 202 to flex so that the bearing surfaces 112 ofthe rotor 302 remain substantially parallel to the bearing surfaces 112of the stator 304 during use.

FIGS. 4A-4C are isometric, top plan, and side cross-sectional views ofan embodiment of a thrust-bearing assembly 400 including a support ringhaving a plurality of radially-extending slots therein configured toreduce warping under operational temperature conditions and flex toaccommodate thermal warping of another thrust-bearing assembly. Thethrust-bearing assembly 400 includes a support ring 202′ similarlyconfigured to the support ring 202 of the thrust-bearing assembly 200shown in FIGS. 2A-2D. However, in addition to thecircumferentially-extending recess 212, the support ring 202′ alsoincludes a plurality of thermal-warping-reducing features 402, whichcompared to if they were absent, increase the compliance of the supportring 202′ and reduce a radial moment that is thermal induced in thesupport ring due to a temperature gradient in the support ring 202′.

In the illustrated embodiment, each thermal-warping-reducing feature 402is configured as a radially-extending slot that extends only partiallythrough the support ring 202′ in a thickness direction. Eachradially-extending slot 402 may be disposed between immediately adjacentsuperhard bearing elements 106. For example, each radially-extendingslot 402 may exhibit a width of about 0.0020 inch to about 0.100 inch,such as about 0.030 inch to about 0.050 inch, about 0.035 inch to about0.045 inch, or about 0.010 inch to about 0.040 inch. However, in otherembodiments, at least one, a portion of, or all of thethermal-warping-reducing features 402 may be configured as a recess, ablind or through hole, or other feature that departs from the depictedelongated geometry of the radially-extending slots. As previouslydiscussed, the radially-extending slots 402 increase the compliance ofthe support ring 202′ compared to if they were absent. By increasing thecompliance of the support ring 202′, a radial moment that is thermallyinduced in the support ring 202′ due to the temperature gradient in thesupport ring 202′ may also be reduced enabling the bearing surfaces 112of the superhard bearing elements 106 to be displaced out of the plane(if at all) by a relatively small amount.

In some embodiments, both the stator and rotor of a thrust-bearingapparatus may be configured as the thrust-bearing assembly 400. In otherembodiments, either the rotor or the stator of a thrust-bearingapparatus may be configured as the thrust-bearing assembly 400.

As an alternative to or in addition to employing radially-extendingslots as thermal-warping-reducing features to reduce thermal warping ofa thrust-bearing assembly when exposed to elevated operationaltemperature conditions, the support ring may be made from a bi-materialstructure that is designed to compensate for the thermal expansionmismatch with the superhard bearing elements 106. FIG. 5 is a sidecross-sectional view of an embodiment of a thrust-bearing assembly 500having a bi-material support ring 502 that is configured to compensatefor thermal warping due to a temperature gradient in the support ring502. The thrust-bearing assembly 500 may be used as in combination withthe thrust-bearing assembly 200 shown in FIGS. 2A-2D to form athrust-bearing apparatus. The support ring 502 is configured similarlyto the support ring 102 shown in FIGS. 1A-1D so only the differencesbetween the support rings 102 and 502 are discussed in the interest ofbrevity.

The support ring 502 includes a first ring portion 504 including aplurality of circumferentially-spaced recesses 506, with each recess 506having one of the superhard bearing elements 106 mounted partiallytherein. The first ring portion 504 exhibits a first thermal expansioncoefficient that is less than that of a second ring portion 508 that isbonded to the first ring portion 504. For example, the first ringportion 504 may comprise an iron-based alloy, such as stainless steel orcarbon steel. The second ring portion 508 exhibits a second thermalexpansion coefficient that is greater than that of the first thermalexpansion coefficient the first ring portion 504. The second ringportion 508 may comprise, for example, a copper alloy, an aluminumalloy, brass, or another suitable material with a thermal expansioncoefficient that is greater than that of the first ring portion 504. Thethickness of the first ring portion 504 may be approximately the same asthe thickness of the second ring portion 508.

When the thrust-bearing assembly 500 is exposed to operationaltemperature conditions, the second ring portion 508 induces athermally-induced radial moment that counters the thermally-inducedradial moment due to the thermal gradient in the support ring 502 sothat the bearing surfaces 112 are displaced out of plane (if at all)about the same extent or less than in the thrust-bearing assembly 100.Accordingly, the second ring portion 508 is configured with a thicknessand a coefficient of thermal expansion so that the thermally-inducedradial moment counters the thermally-induced radial moment due to atemperature gradient in the support ring 502, with temperatureincreasing with distance toward the bearing surfaces 112 of thesuperhard bearing elements 106 (i.e., the temperature is hottest at thebearing surfaces 112). Thus, the second ring portion 508 functions as athermal-warping-reducing feature.

The support ring 502 may be manufactured by a number of differentprocesses. For example, the first and second ring portions 504 and 508may formed integrally together via a powder metallurgy process orseparately formed and joined together via brazing, diffusion bonding,mechanical fastening, or another suitable joining technique.

Although the bearing assembly and apparatus embodiments discussed aboveare for thrust-bearing assemblies and apparatuses. The teachings of thebearing assembly and apparatus embodiments discussed above may beadapted to radial bearing assemblies and apparatuses.

Testing was performed to measure the break-in time for the bearingsurfaces of the thrust-bearing apparatuses configured in accordance withvarious embodiments of the invention. The break-in time is the time atwhich the bearing surfaces of the rotor and stator of the thrust-bearingapparatus are uniformly worn. The break-in time is indicative of theability of the stator and/or the rotor to accommodate misalignmentbetween the bearing surfaces. A lower break-in time may correlate withimproved hydrodynamic performance.

The bearing elements of the thrust-bearing apparatuses tested were PDCshaving approximately a 0.528 inch diameter and an unleachedpolycrystalline diamond table. During the testing, the rotor was rotatedat about 400 RPM and the thrust load was ramped up to about 25,000pounds in about 15 minutes. The thrust load of about 25,000 pounds wasmaintained for about 30 minutes, after which the bearing surfaces wereexamined visually to determine how the bearing surfaces had worn. Afterexamination of the bearing surfaces, the loading and visual inspectionwas repeated, as previously described, until the bearing surfaces wereuniformly worn (i.e., broke in).

Table I below lists the configurations of the thrust-bearing apparatusestested. “Nonconforming” means that the stator or rotor lackedradially-extending slots 116 as shown in the thrust-bearing assembly 100of FIGS. 1A-1D and lacked a circumferentially-extending recess 212 asshown in FIGS. 2A-2D. In Table I below, when the stator or rotorconfiguration recites “conforming,” it means that the support ringincluded a circumferentially-extending recess similar to thecircumferentially-extending recess 212 of the thrust-bearing assembly200 shown in FIGS. 2A-2D. In Table I below, when the stator or rotorconfiguration recites “slots,” it means that the support ring includedradially-extending slots between circumferentially adjacent PDCs similarto the radially-extending slots 116 shown in the thrust-bearing assembly100 of FIGS. 1A-1D. In Table I below, when the stator or rotorconfiguration recites “slots and conforming,” it means that the supportring included radially-extending slots between circumferentiallyadjacent PDCs similar to the radially-extending slots 116 shown in thethrust-bearing assembly 100 of FIGS. 1A-1D and that the support ringalso included a circumferentially-extending recess similar to thecircumferentially-extending recess 212 of the thrust-bearing assembly200 shown in FIGS. 2A-2D.

TABLE I Break-in-Times for Various Thrust-Bearing Apparatus EmbodimentsThrust-Bearing Stator Rotor Break-in Time Apparatus No. ConfigurationConfiguration (hours) 1 nonconforming nonconforming 4 2 conformingconforming 2 3 conforming nonconforming 2.5 4 nonconforming conforming1.5 5 slots slots 1.5 6 conforming slots 4 7 slots conforming 2 8nonconforming slots 3.5 9 slots nonconforming 2 10 slots and conformingnonconforming 1.5 11 slots and conforming slots 1 12 slots andconforming conforming 1

As shown in the test data of Table I, the thrust-bearing apparatus nos.11 and 12 had the lowest break-in time. Consequently, it is believed thethrust-bearing apparatus nos. 11 and 12 will have the best hydrodynamicperformance.

It is currently believed by the inventors that the ability of the rotorand/or the stator to flex and/or to reduce thermal warping helps enablea fluid film to develop during use and make hydrodynamic operationpossible. For example, testing of thrust-bearing apparatuses structuredand fabricated in accordance with one or more embodiments of theinvention have shown as the axial load between the rotor and the statoris linearly increased, the torque required to continue rotating therotor at a given rotation rate increases dramatically at a certain loadindicative of a fluid film breaking down between the bearing surfaces ofthe rotor and the stator. Thus, with a significant enough axial load,the test data indicated that the operation of the thrust-bearingapparatus changes from hydrodynamic operation to non-hydrodynamicoperation in which the bearing surfaces of the rotor and the stator arein physical contact with each other due to the breakdown of the fluidfilm. One reason that the ability of the disclosed thrust-bearingapparatuses to operate in the hydrodynamic operating regime isunexpected is because the stator of such thrust-bearing apparatusincludes a plurality of discrete bearing surfaces and superhard bearingelements (see bearing surfaces 112 of superhard bearing elements 106 inFIG. 1A) as opposed to a continuous bearing surface.

Any of the embodiments for thrust-bearing apparatuses disclosed hereinmay be used in a subterranean drilling system. FIG. 6 is a schematicisometric cutaway view of a subterranean drilling system 600 thatincludes one or more of the disclosed thrust-bearing apparatuses, suchas the thrust-bearing apparatus 300 shown in FIGS. 3A and 3B. Thesubterranean drilling system 600 includes a housing 602 enclosing adownhole drilling motor 604 (i.e., a motor, turbine, or any other devicecapable of rotating an output shaft) that is operably connected to anoutput shaft 606. A first thrust-bearing apparatus 300 ₁ (FIG. 3A) isoperably coupled to the downhole drilling motor 604. A secondthrust-bearing apparatus 300 ₂ (FIG. 3A) is operably coupled to theoutput shaft 606. A rotary drill bit 608 configured to engage asubterranean formation and drill a borehole is connected to the outputshaft 606. The rotary drill bit 608 is shown as a roller cone bitincluding a plurality of roller cones 610. However, other embodimentsmay utilize different types of rotary drill bits, such as a so-called“fixed cutter” drill bit. As the borehole is drilled with the rotarydrill bit 608, pipe sections may be connected to the subterraneandrilling system 600 to form a drill string capable of progressivelydrilling the borehole to a greater depth within the earth.

A thrust-bearing assembly 302 of the thrust-bearing apparatus 300 ₁ isconfigured as a rotor that is attached to the output shaft 606 androtates with the output shaft 606 and a thrust-bearing assembly 304 ofthe thrust-bearing apparatus 300 ₁ is configured as a stator that doesnot rotate. The on-bottom thrust generated when the drill bit 608engages the bottom of the borehole may be carried, at least in part, bythe first thrust-bearing apparatus 300 ₁. A thrust-bearing assembly 302of the thrust-bearing apparatus 300 ₂ is configured as a rotor that isattached to the output shaft 606 and rotates with the output shaft 606and a thrust-bearing assembly 304 of the thrust-bearing apparatus 300 ₂is configured as a stator that does not rotate. Fluid flow through thepower section of the downhole drilling motor 604 may cause what iscommonly referred to as “off-bottom thrust,” which may be carried, atleast in part, by the second thrust-bearing apparatus 300 ₂.

In operation, drilling fluid may be circulated through the downholedrilling motor 604 to generate torque and effect rotation of the outputshaft 606 and the rotary drill bit 608 attached thereto so that aborehole may be drilled. A portion of the drilling fluid may also beused to lubricate opposing bearing surfaces of the bearing elements 106of the thrust-bearing assemblies 302.

Although the thrust-bearing assemblies and thrust-bearing apparatusesdescribed above have been discussed in the context of subterraneandrilling systems and applications, in other embodiments, thethrust-bearing assemblies and thrust-bearing apparatuses disclosedherein are not limited to such use and may be used for many differentapplications, if desired, without limitation. Thus, such thrust-bearingassemblies and thrust-bearing apparatuses are not limited for use withsubterranean drilling systems and may be used with various othermechanical systems, without limitation.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting. Additionally, the words “including,”“having,” and variants thereof (e.g., “includes” and “has”) as usedherein, including the claims, shall have the same meaning as the word“comprising” and variants thereof (e.g., “comprise” and “comprises”).

What is claimed is:
 1. A bearing assembly for use in a subterraneandrilling system, comprising: a plurality of superhard bearing elementsdistributed circumferentially about an axis, each of the plurality ofsuperhard bearing elements including a superhard bearing surface, thesuperhard bearing surfaces of the plurality of superhard bearingelements being substantially coplanar with each other; and a supportring having a plurality of recesses each extending inwardly andterminating at a first depth, each of the plurality of superhard bearingelements mounted at least partially within a corresponding one of theplurality of recesses, the support ring including, a plurality ofradially-extending slots formed in the support ring, each of theplurality of radially-extending slots disposed between immediatelycircumferentially adjacent ones of the plurality of superhard bearingelements, each of the plurality of radially-extending slots extendinginto the support ring to at least the first depth, thereby increasingcompliance of the support ring, during use, compared to if the pluralityof radially-extending slots were not present in the support ring.
 2. Thebearing assembly of claim 1 wherein the plurality of radially-extendingslots are configured to reduce the radial moment, compared to if theplurality of radially-extending slots were absent from the support ring,when the support ring and the plurality of superhard bearing elementsare exposed to the operational temperature conditions so that thesuperhard bearing surfaces remain substantially coplanar with a maximumflatness of about 0.00020 inch to about 0.0020 inch.
 3. The bearingassembly of claim 1 wherein each of the plurality of radially-extendingslots is disposed circumferentially between a respective pair ofimmediately circumferentially adjacent ones of the plurality ofsuperhard bearing elements.
 4. The bearing assembly of claim 1 whereineach of the radially-extending slots exhibit a width greater than about0.0020 inch.
 5. The bearing assembly of claim 4 wherein the width isabout 0.0020 inch to about 0.100 inch.
 6. The bearing assembly of claim4 wherein the width is about 0.010 inch to about 0.040 inch.
 7. Thebearing assembly of claim 1 wherein each of the plurality ofradially-extending slots is disposed circumferentially about halfwaybetween the immediately adjacent ones of the plurality of superhardbearing elements.
 8. The bearing assembly of claim 1 wherein the supportring comprises: an upper base that extends circumferentially and onwhich the plurality of superhard bearing elements are supported; a lowerbase; and a flexible support that extends between the upper base and thelower base.
 9. The bearing assembly of claim 1 wherein at least aportion of the plurality of superhard bearing elements comprises asubstrate and a superhard table bonded to the substrate.
 10. The bearingassembly of claim 9 wherein the superhard table comprisespolycrystalline diamond.
 11. The bearing assembly of claim 1 whereineach of the plurality of superhard bearing elements is brazed,interference-fitted, or fastened to the support ring.
 12. The bearingassembly of claim 1 wherein the operational temperature conditions areabout 100° C. to about 200° C.
 13. The bearing assembly of claim 1wherein the axis is a thrust axis, and wherein the support ring and theplurality of superhard bearing elements define a thrust-bearingassembly.
 14. The bearing assembly of claim 1 wherein the plurality ofradially-extending slots extend into the support ring to at least asecond depth that is greater than the first depth.
 15. A bearingapparatus for use in a subterranean drilling system, comprising: a firstbearing assembly including, a plurality of first superhard bearingelements distributed circumferentially about an axis and having aplurality of substantially coplanar superhard bearing surfaces; and afirst support ring having the plurality of first superhard bearingelements mounted within recesses that terminate at a first depth in thefirst support ring, the first support ring including, at least onethermal-warping-reducing feature configured to reduce a radial moment,compared to if the at least one thermal-warping-reducing feature wereabsent from the support ring, the radial moment being thermally inducedin the first support ring when the support ring and the plurality offirst superhard bearing elements are exposed to operational temperatureconditions, the at least one thermal-warping-reducing feature configuredto increase compliance of the first support ring and to allow theplurality of first superhard bearing elements to move out of plane byabout 0.02 degrees to 0.2 degrees responsive to the radial moment, theat least one thermal-warping-reducing feature including a slot extendinginto the support ring to at least the first depth; and a second bearingassembly including a plurality of second superhard bearing elementsgenerally opposing the plurality of first superhard bearing elements ofthe first bearing assembly and distributed circumferentially about theaxis.
 16. The bearing apparatus of claim 15 wherein the first bearingassembly is configured as a stator, and the second bearing assembly isconfigured as a rotor, the second thrust-bearing assembly including, asecond support ring having the plurality of superhard bearing elementsmounted thereto, the second support ring including, a base that extendscircumferentially and on which the plurality of superhard bearingelements are mounted; a lower base; and a flexible support that extendsbetween the upper base and the lower base.
 17. The bearing apparatus ofclaim 15 wherein the first support ring comprises: a base that extendscircumferentially and on which the plurality of first superhard bearingelements are mounted; a lower base; and a flexible support that extendsbetween the upper base and the lower base.
 18. A motor assembly for usein a subterranean drilling system, comprising: a motor operable to applytorque to a rotary drill bit; and a bearing apparatus operably coupledto the motor, the bearing apparatus including a rotor and a stator; andwherein at least one of the rotor or the stator comprises: a pluralityof superhard bearing elements distributed circumferentially about anaxis, each of the plurality of superhard bearing elements including asuperhard bearing surface, the superhard bearing surfaces of theplurality of superhard bearing elements being substantially coplanarwith each other; and a support ring having a plurality of recesses eachextending inwardly and terminating at a first depth, each of theplurality of superhard bearing elements mounted at least partiallywithin a corresponding one of the plurality of recesses, the supportring including, a plurality of radially-extending slots formed in thesupport ring, each of the plurality of radially-extending slots disposedbetween immediately circumferentially adjacent ones of the plurality ofsuperhard bearing elements, each of the plurality of radially-extendingslots extending into the support ring to at least the first depth,thereby increasing compliance of the support ring.
 19. A method ofoperating a bearing apparatus in a subterranean drilling system,comprising: providing a first bearing assembly including, a plurality offirst superhard bearing elements distributed circumferentially about anaxis, each of the plurality of superhard bearing elements including asuperhard bearing surface, the superhard bearing surfaces of theplurality of superhard bearing elements being substantially coplanarwith each other; and a first support ring having a plurality of recesseseach extending inwardly and terminating at a first depth, each of theplurality of first superhard bearing elements mounted at least partiallywithin a corresponding one of the plurality of recesses, the supportring including, a plurality of radially-extending slots formed in thesupport ring, each of the plurality of radially-extending slots disposedbetween immediately circumferentially adjacent ones of the plurality ofsuperhard bearing elements, each of the plurality of radially-extendingslots extending into the support ring to at least the first depth;providing a second bearing assembly including, a plurality of secondsuperhard bearing elements generally opposing the plurality of firstsuperhard bearing elements of the first bearing assembly and distributedcircumferentially about the axis; operating the bearing apparatus underhydrodynamic operational conditions in which a fluid film developsbetween the plurality of first superhard bearing elements and theplurality of second superhard bearing elements that prevents contacttherebetween; and wherein the plurality of radially-extending slotsincrease compliance of the first support ring.
 20. The method of claim19, further comprising operating the bearing apparatus undernon-hydrodynamic operational conditions in which the fluid film betweenthe plurality of first superhard bearing elements and the plurality ofsecond superhard bearing elements does not prevent contact between theplurality of first superhard bearing elements and the plurality ofsecond superhard bearing elements.
 21. A thrust-bearing assembly,comprising: a plurality of superhard bearing elements distributedcircumferentially about an axis; a support ring having the plurality offirst superhard bearing elements mounted within recesses that terminateat a first depth in the support ring, the plurality of first superhardbearing elements having a plurality of superhard bearing surfaces thatlie substantially on the same imaginary surface, the support ringincluding, at least one thermal-warping-reducing feature configured toreduce a radial moment, compared to if the at least onethermal-warping-reducing feature were absent from the support ring, theradial moment being thermally induced in the support ring when thesupport ring and the plurality of superhard bearing elements are exposedto operational temperature conditions, the at least onethermal-warping-reducing feature configured to increase compliance ofthe support ring and to allow the plurality of superhard bearingelements to move out of plane by about 0.02 degrees to 0.2 degreesresponsive to the radial moment, the at least onethermal-warping-reducing feature including a slot extending into thesupport ring to at least the first depth.